Elements for Kids
Arsenic is the third element in the fifteenth column of the periodic table. It is classified as a metalloid because it has some properties similar to a metal and others of a non-metal. Arsenic atoms have 33 electrons and 33 protons with 5 valence electrons in the outer shell.
- Symbol: As
- Atomic Number: 33
- Atomic Weight: 74.92
- Classification: Metalloid
- Phase at Room Temperature: Solid
- Density: 5.727 grams per cm cubed
- Melting Point: 817°C, 1503°F
- Boiling Point (Sublimation Point): 614°C, 1137°F
- Discovered by: Albertus Magnus in 1250
Characteristics and Properties
Arsenic exists in a number of allotropes. Allotropes are different structures of the same element. Although they are made up of the same element, their different structures can have very different characteristics. For example, carbon has the allotropes graphite and diamond.
Arsenic's two most common allotropes are yellow and metallic gray. Gray arsenic is a brittle shiny solid. Yellow arsenic is soft and waxy. Yellow arsenic is reactive and very toxic. It converts to gray arsenic when exposed to light at room temperatures. Another allotrope is black arsenic.
How poisonous is arsenic?
Arsenic is perhaps most famous for its high toxicity. This means that it is very poisonous. Many of its compounds are poisonous as well. Too much arsenic can quickly kill a person and it has been used in assassinations throughout history. Also, exposure to small amounts of arsenic over time can cause many health issues. There are many laws on how arsenic should be handled and disposed of when used in industry.
Where is it found on Earth?
Arsenic is found in the Earth's crust. It can be found in its free form, but this is rare. Most arsenic exists in minerals such as realgar, mispickel (arsenopyrite), and orpiment. Arsenic for industrial use is generally produced as a byproduct from mining gold, silver, and copper.
How is arsenic used today?
Arsenic has been used in the past as an insecticide as well as a wood preservative. Because of environmental issues it is no longer used as an insecticide and is being phased out as a wood preservative in the United States. As a wood preservative, the compound copper arsenate helped to stop wood from rotting and also kept termites and other insects from destroying the wood.
Arsenic is combined with gallium to produce gallium arsenide for use in high speed electronics and optoelectronics. Other applications for arsenic include metal alloys and glass making.
How was it discovered?
Arsenic has been known about since ancient times as part of a compound with sulfur. It is thought that it was first isolated during the Middle Ages by German philosopher Albertus Magnus in 1250.
Where did arsenic get its name?
Arsenic may have gotten its name from the Greek word "arsenikon" which means "yellow pigment" or "arsenikos" which means "potent."
Arsenic occurs in nature in one stable isotope which is arsenic-75.
Interesting Facts about Arsenic
- When it is heated in air it combines with oxygen to produce arsenic trioxide.
- Despite how poisonous arsenic is, a very small amount is considered important for the health of animals.
- Arsenic doesn't melt under standard pressure, but sublimes directly into gas. It only melts under high pressure.
- We recommend that you NEVER use, handle, or experiment with arsenic or its compounds. It is very dangerous.
More on the Elements and the Periodic Table
More Chemistry Subjects